Eye on the Prize: Master Physiological Optics with NBEO Practice Test 2026!

The effect comes from geometry of how you look through a magnifier. The linear field of view through a handheld magnifier is basically the width of the scene you can see through the lens at a given working distance, and it depends on the angle the eye subtends to the lens. When you move the lens closer to the eye, that angle becomes larger, so more of the scene passes through the edges of the lens and into the eye. In other words, the eye can sample a wider portion of the image through the lens, so the linear field of view increases. If you pull the magnifier away from the eye, the angular span shrinks and the field narrows.